Historically, first crude oils, then diesel oils and, more recently, mineral oils have been used in formulating well fluids. Due to problems of toxicity and persistence which are associated with these oils, and which are of special concern of offshore use, the industry is developing well fluids which are based on "pseudo-oils". Examples of such oils are fatty acid esters and synthetic hydrocarbons such as poly(alpha)olefins. Fatty acid ester based oils have excellent environmental properties, but well fluids made with these esters tend to have lower densities and are prone to hydrolytic instability. Poly(alpha)olefin based well fluids can be formulated to high densities, have good hydrolytic stability and low toxicity. They are, however, somewhat less biodegradable than esters, they are expensive and the fully weighted, high density fluids tend to be overly viscous, especially when used in cold climates. A most recent trend in the industry is the use of base oils comprising mixtures of predominantly linear internal olefins. Well fluid base oils comprised of mainly linear internal olefins are acceptably environmentally friendly and have pour point temperatures in the range of about -10.degree. C. which is borderline for cold climates. What is needed is an environmentally acceptable well fluid base oil having a pour point lower than -25.degree. C. The present invention addresses this need.